style_add
style_add(dgc, oo, "pane-border-style", ft);
style_add(gc, oo, name, ft);
struct style *style_add(struct grid_cell *, struct options *,
sy = style_add(&wp->cached_active_gc, oo, "window-active-style", ft);
sy = style_add(&wp->cached_gc, oo, "window-style", ft);